1. Field of the Invention
The present invention relates generally to an alignment pin for aligning two structures that are to be joined or mated. Specifically, the present invention relates to an alignment pin providing a greatly reduced potential for binding and, more particularly, to a non-binding alignment pin for use in aligning a test head with a semiconductor device handler while docking the test head to the handler.
2. State of the Art
Electrical, functional, and environmental testing is an important facet of semiconductor device manufacturing. Semiconductor devices, such as bare semiconductor die and packaged integrated circuit chips, are routinely subjected to a wide array of tests directed to screening out damaged or defective devices and to measuring the operational characteristics of a device for classification and subsequent sorting. In order to facilitate handling of a large number of semiconductor devices during production, the handling and testing of semiconductor devices is usually automated. Automated equipment for handling, testing, and sorting semiconductor devices is well known in the art.
Shown schematically in FIG. 1 is an exemplary typical semiconductor device test system 5. The test system 5 includes a handler 10 and a test head 20, which are shown in an undocked, or separated, condition. The handler 10 is configured to receive semiconductor devices from a sourcexe2x80x94for example, a tube or a trayxe2x80x94and to unload the semiconductor devices onto a transport medium, such as a boat. The handler 10 then transports the semiconductor devices to a test station 12 for testing. Also, the handler 10 may thermally condition the semiconductor devices prior to testing. At the test station 12, the handler 10 positions the semiconductor devices such that leads extending from each individual semiconductor device are in electrical contact with a plurality of test contacts extending from the test head 20. In order to obtain reliable test data, robust and reliable electrical contact must be maintained between the semiconductor device leads and the test contacts 30 of the test head 20.
A significant factor affecting the electrical connection between the leads of a semiconductor device and the corresponding test contacts 30 on the test head 20 is alignment between the test head 20 and the handler 10 and, hence, the alignment between the test contacts 30 and the semiconductor device leads. Thus, docking of the test head 20 onto the handler 10 is a critical procedure as the test head 20, and the test contacts 30 extending therefrom, must be precisely aligned with respect to the handler 10. Even the slightest misalignment between the handler 10 and test head 20 can result in poor, or even no, electrical contact between the test contacts 30 and the leads of a plurality of semiconductor devices positioned in the test station 12 for testing. Also, the size and weight of the test head 20 are typically very large, often necessitating the use of mechanical lifting equipment for maneuvering the test head 20 during docking. Because of the significant weight of the test head 20, any misalignment between the test head 20 and handler 10 during a docking operation can result in damage to both the handler 10 and test head 20, and particularly to the test contacts 30. Damaged test contacts 30 will, most likely, provide unreliable electrical contact with mating semiconductor device leads.
From the foregoing discussion, one of ordinary skill in the art will understand the importance of maintaining precise alignment between the test head 20 and handler 10 while docking the test head 20 onto the handler 10. One method for maintaining alignment of the test head 20 relative to the handler 10 is the use of alignment pins 15, as shown in FIG. 1. The alignment pins 15, which are shown attached to the handler 10, mate with corresponding holes 25 in the test head 20. Although shown affixed to the handler 10, the alignment pins 15 may be attached to the test head 20 and, accordingly, the mating holes 25 disposed in the handler 10. Typically, as shown in FIG. 1, two alignment pins 15 are used to provide the necessary alignment between the test head 20 and handler 10; however, only one alignment pin 15 or more than two alignment pins 15 may be employed. Also, to provide precise alignment between the test head 20 and handler 10, the design tolerancesxe2x80x94size, orientation, and positionxe2x80x94of the alignment pins 15 and mating holes 25 are generally relatively small in comparison to the overall dimensions of the test head 20 and handler 10.
The use of alignment pins 15, however, may itself cause problems during semiconductor device testing resulting from binding between the alignment pins 15 and mating holes 25. Generally, binding may be thought of as the braking, or even seizure, of one body relative to another body due to high contact pressure existing between the two bodies. Binding of the alignment pins 15 and mating holes 25 may result in unreliable electrical contact between the test contacts 30 and the leads of a semiconductor device, damage to the test contacts 30, damage to other portions of the test head 20 and handler 10, and damage to the semiconductor devices positioned at the test station 12 for testing. Also, binding between the alignment pins 15 and mating holes 25 can make undocking of the test head 20 difficult, as the binding may essentially xe2x80x9clockxe2x80x9d the test head 20 to the handler 10. Further, binding of the alignment pins 15 within the holes 25 can damage the alignment pins 15 themselves, which may exacerbate the effects of binding.
Although the present invention is particularly concerned with the problem of alignment and binding between a semiconductor device handler and test head, as described above, the present invention is applicable to the use of alignment pins to align any types of structures. Thus, the following discussion pertaining to the conditions that may cause binding are generally applicable to the alignment of any two bodies using alignment pins or other alignment structures.
For mating structures, such as an alignment pin and mating hole, binding is generally due to interference between surfaces of the mating structures and can result from any one of a number of interference conditions, or binding modes, that may exist between the surfaces. Binding modes may be generally classified into four types: (1) those due to design or manufacturing tolerances, (2) those due to positioning errors during joining, (3) those due to thermal effects, and (4) those due to wear and damage. The foregoing binding modes, however, are not all-inclusive and those of ordinary skill in the art will understand that binding may result from conditions other than those described herein.
Binding may result from the unwise selection of design tolerances or from the failure to adhere to design tolerances during manufacture. In either case, interference may result between a surface of an alignment pin and a surface of a mating hole. Such interference may, for example, result from an oversized pin, an undersized hole, or, as shown in FIG. 2, a circular pin 65 extending from a first body 60 mating with a non-concentric hole 75 in a second body 70. Errors in feature location tolerances may also lead to binding. Referring to FIG. 3, a first body 60 includes a plurality of alignment pins 65 extending transversely therefrom. A second body 70 includes a plurality of holes 75 configured for mating with the alignment pins 65 to align the first and second bodies 60, 70. However, due to tolerancing or manufacturing errors, an alignment pin 65xe2x80x2 and hole 75xe2x80x2 are out of alignment. For example, the centers of the pin 65xe2x80x2 and hole 75xe2x80x2 may be linearly offset by a distance 81 or angularly offset through an angle 91.
Binding resulting from errors in design and manufacturing tolerances may also result from a failure to properly orient an alignment pin or mating hole, or both. Referring to FIG. 4, a first body 60 includes a plurality of alignment pins 65 extending from a surface thereof. A second body 70 includes a plurality of holes 75 configured for mating with the alignment pins 65 of the first body 60. One of the alignment pins 65 is incorrectly orientated through an angle 92 relative to its corresponding hole 75 in the second body 70. Similarly, one of the holes 75 is incorrectly orientated through an angle 93 relative to a mating pin 65 extending from the first body 60. For clarity, the errors in orientation depicted in FIG. 4 are shown only in one plane; however, one of ordinary skill in the art will understand that such errors may occur in multiple planes.
Positioning errors present during joining of two bodies may also result in binding. For example, as shown in FIGS. 5 through 7, two bodies may be improperly aligned during joining. Referring to FIGS. 5 and 6, a first body 60 includes a plurality of alignment pins 65 extending therefrom configured for insertion into corresponding holes 75 in a second body 70. However, the two bodies 60, 70 may be linearly offset by a distance 82 (see FIG. 5) or angularly offset through an angle 94 (see FIG. 6). Similarly, two bodies may be improperly orientated during joining. Referring to FIG. 7, a second body 70 is being joined to a first body 60, and the second body 70 includes a plurality of holes 75 configured for receiving a corresponding plurality of alignment pins 65 extending from the first body 60. The second body 70 is, however, improperly orientated through an angle 95 relative to the first body 60. Although FIG. 7 depicts an orientation error in only one plane, those of ordinary skill in the art will understand that such errors can occur in multiple planes.
Thermal expansion effects may also cause binding between an alignment pin and a mating hole. Referring to FIG. 8, a first body 60 includes an alignment pin 65 mating with a corresponding hole 75 in a second body 70. The pin 65 has a diameter 83 at a first, low temperature. If the temperature of the first body 60 and pin 65 increases to a second, relatively higher temperature, the pin 65 may expand to a larger diameter 84 (shown in dashed line). The hole 75 in the second body 70 may not equivalently expand due to differences in relative temperature or differences in materials used to form the two bodies 60, 70. As the pin 65 thermally expands, the diameter of the pin 65 may eventually equal that of the hole 75 resulting in interference between the outer surface of the pin 65 and surface of the hole 75. Further thermal expansion of the pin 65 will cause increasing interference and contact between surfaces of the pin 65 and hole 75, as well as a large pressure build-up therebetween.
Damage, such as galling, to the surface of an alignment pin or a mating hole may also cause binding. Referring to FIGS. 9 and 10, a first body 60 includes and alignment pin 65 configured for mating with a hole 75 in a second body 70 to be joined with the first body 60. As seen in FIG. 9, a portion 68 of the surface of the pin 65 is damaged during joining of the first and second bodies 60, 70 due to, for example, misorientation of the second body 70. Referring to FIG. 10, the orientation of the second body 70 has been corrected and the bodies 60, 70 joined. However, debris 69a sheared from the damaged surface portion 68 of the alignment pin 65 may become lodged between the surface of the alignment pin 65 and the surface of the mating hole 75, resulting in increased frictional forces and possibly jamming between the alignment pin 65 and mating hole 75. Also, the damaged surface portion 68 of the alignment pin 65 may include one or more protrusions 69b extending therefrom and impinging upon the surface of the hole 75 in the second body 70, thereby increasing the potential for binding therebetween.
The design and manufacturing tolerance errors, positioning errors, thermal expansion effects, and damage effects depicted in FIGS. 2 through 10 have been exaggerated for clarity. These tolerancing errors, positioning errors, thermal effects, and damage effects may, in practice, be relatively small in dimension. However, even though such errors and effects may be relatively minor, interference between the respective surfaces of an alignment pin and mating hole can result. Also, it will be appreciated by those of ordinary skill in the art that the binding modes described hereinxe2x80x94tolerancing errors, positioning errors, thermal effects, and damage effectsxe2x80x94may, and most likely will, occur substantially simultaneously and in combination with one another.
Interference between the surfaces of an alignment pin and mating hole may cause immense pressurexe2x80x94especially when aligning heavy structures such as, for example, the test head 20 shown in FIG. 1, which can weigh on the order of 800 to 1000 poundsxe2x80x94at the contact interface between these surfaces, resulting in high frictional forces. High pressure at the contact interface between an alignment pin and mating hole may also lead to adhesion or xe2x80x9ccold weldingxe2x80x9d of a portion of the surface of the alignment pin to the surface of the mating hole. Also, interference between the alignment pin and mating hole may result in the shearing of small particles of material, or debris, from the respective surfaces of the alignment pin and mating hole, as discussed in reference to FIGS. 9 and 10, and the debris itself may cause more interference between the alignment pin and mating hole. Further, the alignment and movement of heavy structures, such as a semiconductor device test head, increases the likelihood of positioning errors, and hence interference, during joining due to the necessity of handling such large, heavy structures with mechanical lifting equipment and the corresponding inability to readily manipulate such structures by hand.
Frictional forces exerted by one structure upon another are generally independent of the apparent surface area of contact (i.e., the area as determined by the overall physical dimensions of the portions of two surfaces in contact) between the two structures. Rather, the forces due to friction are proportional to the real area of contact (i.e., the portions of two surfaces in actual contact at the atomic scale) between the two structures, and the real contact area is proportional to the normal load that the two structures impart to each other. Hence, as is widely known, frictional forces are generally proportional to the normal load. The upper theoretical limit on the real contact area is, of course, bounded by the apparent surface area of contact (although, at its upper limit, the real contact area may exceed the apparent contact area due to surface roughness).
When a very high normal loadxe2x80x94and, therefore, high contact pressurexe2x80x94exists between two structures, the real contact area may approach its upper theoretical limit. Thus, for high contact pressure at the interface between two structures, the overall physical dimensions of the apparent surface area of contact may have an effect upon the magnitude of the frictional forces, and it may be desirable to minimize the physical dimensions of the apparent contact surface area. However, for high contact pressure between the surfaces of two structures, the forces required to overcome adhesion or xe2x80x9ccold weldingxe2x80x9d effectsxe2x80x94those forces being generally proportional to the adhered surface areaxe2x80x94may predominate over those due to friction. Further information relating to the effects of high contact pressure on frictional forces, and to the distinction between real and apparent contact surface area, can found in: Machinery""s Handbook, 23 Ed., at pgs. 2201-2204 (Industrial Press 1989); Friction: An Introduction to Tribology, F. P. Bowden and D. Tabor, at pgs. 47-75 (Anchor Press 1973); and CRC Handbook of Lubrication (Theory and Practice of Tribology), Vol. 11, Theory and Design, at pgs. 31-48 (CRC Press 1983).
Alignment pins known in the art include constant diameter pins and tapered pins having a non-constant diameter. Another prior art alignment pin known to the inventor, for use with a semiconductor device handler and test head as described with reference to FIG. 1, is shown in FIG. 11. The alignment pin 100 is affixed to a handler 10 and is configured to receive thereon a mating hole 25 in a test head 20 (shown in dashed line) to be docked on the handler 10. The alignment pin 100 includes a straight shank portion 110, an enlarged register portion 120, and an upper tapered portion 130. The shank portion 10 has an outer cylindrical surface 112 of a diameter 114. The shank portion 110 also includes a lower end 116 attached to the handler 10 and an upper end 118 terminating adjacent the register portion 120. The register portion 120 includes an outer surface 122 having a diameter 124 of a dimension nearly equal to, but slightly less than, a diameter of the surface 26 of the mating hole 25 in the test head 20. The register portion 120 is essentially a sphere in which, at the lower end 126 joining with the upper end 118 of the shank portion 110, the lower portion of the sphere has been truncated and, at the upper end 128 joining with a lower end 136 of the tapered portion 130, the upper portion of the sphere is similarly truncated. The tapered portion 130 has a non-constant diameter that varies from a maximum at the lower end 136 to a minimum at an upper end 138 of the tapered portion 130, resulting in a cylindrical outer surface 132 that is tapered.
The diameter 124 of the register portion 120 is larger than the diameter 114 of the shank portion 110. As a result, an annular clearance zone 140 (shown in dashed line) exists under the outer surface 122 of the register portion 120 and adjacent the outer surface 112 of the shank portion 110. Providing a clearance zone 140 compensates for some positional error during joining of the test head 20 to the handler 10. By way of example, as shown in FIG. 11, for a test head 20xe2x80x2 (shown in dashed line) and hole 25xe2x80x2 that have an orientation angularly offset from the orientation of the handler 10 and alignment pin 100, the clearance zone 140 can receive a portion 28 of the test head 20xe2x80x2 without interference therebetween, thereby xe2x80x9cabsorbingxe2x80x9d the positional error of the test head 20xe2x80x2 until the orientation of the test head 20xe2x80x2 can be corrected. When the alignment pin 100 and mating hole 25 are fully engaged, the outer surface 122 of the register portion 120 interfaces with the surface 26 of the hole 25 to align the hole 25 relative to the alignment pin 100 and, thus, to align the test head 20 and handler 10.
Use of a plurality of prior art alignment pins 100 to align a test head 20 and handler 10 was found to insufficiently alleviate binding between the alignment pins 100 and a plurality of mating holes 25 in the test head 20. Although the prior art alignment pin 100 may compensate for some positional errorxe2x80x94specifically, error in angular orientationxe2x80x94during joining of a test head 20 to a handler 10, other binding modes are still present and may predominate. Errors in design and manufacturing tolerances, translational errors during joining, thermal effects, and damage on the surfaces of the alignment pins and mating holes may, either individually or in combination, cause interference between the alignment pins and mating holes and, therefore, the generation of high contact pressure.
It is believed that, due to the weight of the test head, interference between respective surfaces of the alignment pins and mating holes causes high pressure regions of contact between the alignment pins and mating holes. These high pressure contact regions between the respective surfaces of the alignment pins and mating holes may result in the development of high frictional forces therebetween. High pressure contact between the alignment pins and mating holes may also be causing adhesion, or xe2x80x9ccold welding,xe2x80x9d of portions of the surface of an alignment pin to portions of the surface of a mating hole. Also, interference between the alignment pins and mating holes may generate debris that becomes lodged between the alignment pins and mating holes.
Accordingly, a need exists in the art for an alignment pin for use in aligning a first body relative to a second body such that, upon joining of the two bodies, binding between a plurality of the alignment pins extending from the first body and a plurality of mating holes in the second body is significantly reduced or eliminated. Further, there is a need in the art for such an alignment pin for use in docking a test head to a semiconductor device handler.
Embodiments of the present invention include a number of embodiments of an alignment pin for use in aligning any two structures that are to be joined or mated, such as a test head and a semiconductor device handler. An alignment pin according to the present invention includes at least one register portion configured for insertion into a mating hole and alignment of the mating hole thereon. The alignment pin further includes a shank portion joined with the register portion and may also include a tapered portion disposed therebetween. An annular region located adjacent an outer surface of the shank portion and above or below an outer surface of the register portion provides a clearance zone, which can compensate for some positional error during the aligning and joining of two structures.
The outer surface of the register portion may comprise a plurality of contact regions circumferentially separated by relief regions. Any suitable number of contact regions may be incorporated at the outer surface of the register portion. The contact regions need not be equidistantly spaced about the outer surface of the register portion and, further, the contact regions may be disposed on the ends of a plurality of fins extending from the register portion and separated on either side by the relief regions. The plurality of alternating contact and relief regions on the outer surface of the register portion minimizes the amount of surface area of the alignment pin actually in contact with the surface of a mating hole. For high pressure contact at the interface between the alignment pin and the surface of a mating hole, reducing the overall physical dimensions of the surface area in contact may result in lower frictional forces and less adhesion. Also, the relief regions on the outer surface of the register portion act as xe2x80x9cjunk slots,xe2x80x9d providing channels or passages between the register portion and the bore wall of a mating hole for efficiently removing debris from the interface between the alignment pin and the mating hole. Reduced frictional forces at the contact interface between one or more alignment pins and a corresponding number of mating holes, in conjunction with the efficient removal of debris, will reduce the severity of binding that may potentially occur between the alignment pins and mating holes.